I. Technical Field
This invention relates generally to the field of agriculture and molecular biological modification of crops. Specifically, this invention relates to a method for enhancing quality factors in plants and particularly in cotton (e.g., Gossypium hirsutum L., G. barbadense L., G. arboreum and G. herbaceum). In preferred embodiments, the invention involves generating transgenic cotton plants that contain genetic systems to suppress seed-oil, protein and/or macronutrients, such as nitrogen (N), phosphorous (P) and potassium (K) in cotton seed. These preferred embodiments involve producing transgenic cotton plants that contain within their genomes genetic systems that modulate, suppress or deactivate the storage systems for oil, protein, phytate and/or macronutrients when a plant is grown to produce fiber. Particular preferred embodiments provide a method for generating transgenic cotton plants that contain a dominant negative allele for an endoplasmic reticulum located protein, which provides cotton plants with lower seed storage reserve content, increased fiber yields and reduced need for macronutrients.
II. Description of the Background Art
Fiber yield enhancement using traditional plant breeding techniques has been an important objective of cotton breeding. As a result of intense breeding selection for genetic improvements in fiber yield, the genetic contribution to fiber yield and lint percent (ratio of fiber to fiber-plus-seed) has increased during the last 50 years. Transgenic technology provides new opportunities to accelerate the genetic yield gain beyond those possible using traditional methods because this technology can alter the metabolic machinery of the plant. Efforts to enhance fiber yield in cotton with transgenic technology have involved, for example, manipulating plant hormones and stress and disease tolerance. Other methods for enhancing cotton yield have been reported by Hake et al., U.S. Published Patent Application 2004/0133944 and Lauterback et al., “Yield enhancement in cotton,” in Genetic Control of Cotton Fiber and Seed Quality, Cotton Incorporated, Cary, N.C., 2000. Transgenic technologies, such as sense suppression, antisense suppression and RNA interference methods, have been used to modify seed constituents in cotton. Seed oil modification in cotton for altering fatty acid profiles has been an active area of research. See Chapman et al., J. Am. Oil Chemists Soc., 78:941-947, 2001; Liu et al., Plant Physiol. 129:1732-1743, 2002.
Yield enhancement technology in field crops has been an active area in plant biology research. However, in cotton the complexity and uniqueness of the harvestable product, bolls of cotton fiber, has provided special challenges. Modern chemical and biotechnological technologies for managing insect pests, combined with reduced season-length production strategies, have improved the percent boll set and the rate of sucrose utilization in fiber development in cotton. However, methods are still needed to further improve cotton plant qualities, including fiber yield enhancement, and other plant characteristics that increase the efficiency of cultivation of this important crop.
It is generally understood by those of skill in the art of plant cultivation, that cotton requires lower inputs of fertilizers than other commercial crops. This is in part due to the temporary storage in leaves of mineral nutrients needed by cotton seeds as they develop. In addition, cotton fiber is largely cellulose. Thus, input of significant amounts of macronutrients to the plant prior to anthesis and boll filling is required which results in the temporary storage of macronutrients in leaves and the resulting elevated nutrition for insect pests feeding on preanthesis cotton leaves.
Nevertheless, mineral nutrients in the soil where cotton is grown do become depleted, and the application of commercial fertilizers is eventually required, particularly where cotton is grown in rotation with other commercial crops such as corn, ground nuts, cassaya, millet, rice and grain legumes. In developing countries resources needed to purchase fertilizer could be diverted from those available for essential human needs such as shelter, medicine, food and education.
Advances in agricultural technology have provided new plant varieties that require reduced tillage of the soil. However, reduced tillage also results in the reduced availability of macronutrients. This is particularly true where plant debris or litter remaining after harvest is not tilled or plowed back into the soil. A recent study has shown that approximately 46% of the nitrogen from cotton litter is released into the soil during the four month period after it is incorporated or plowed under in a field. Only about 19% is released when no-till methods are used. (See Lachnicht et al., 2004). Thus, application of increased amounts of fertilizer or elevated soil nutrient availability is required for no till crop rotations.
The availability of new varieties of cotton that require lower amounts of fertilizer would further improve the efficiency of cultivation methods, particularly in developing countries where resources are scarce. Thus, new varieties with traits that provide reduced levels of stored mineral macronutrients are desired.
The need for the addition of the macronutrient phosphorous back to the soil results in part from the accumulation of phytate (phytic acid or inositol-hexaphosphoric acid) in seed. In plants phytate is metabolized into inorganic phosphate, which is utilized in energy transfer. However, non-ruminant animals do not efficiently metabolize phytate. Phytates from seeds used in animal feeds can contaminate manure and be leached into streams, lakes and oceans where microbial degradation of the compound releases phosphate, which in turn can lead to algal growth and eutrification (anaerobisis, oxygen deprivation) of bodies of water. (See Ferber 2004; Leigh 2004.) Phosphate and nitrogen runoff from agriculture in the central United States into rivers and the Gulf of Mexico is recognized as a major source of eutrification of the fish habitat in those bodies. Thus, plants and methods for producing those plants with decreased storage of phosphorus in the form of phytate are desired.